This invention concerns projection television systems utilizing color cathode ray picture tubes, and is particularly directed to systems in which discrete images are projected on a viewing screen to form a composite color picture.
A projection television system of this type is described and fully claimed in referent copending application Ser. No. 459,004 . A jack-in-the-box projection television receiver comprises a cabinet for enclosing the components of the receiver, and includes a lid hinged at the back of the cabinet. The receiver includes a vertically arranged, elevatable rear projection screen selectively storable in the cabinet. Image source means provide for forming a television image. Stationary optical assembly means provide for projecting an aerial image of a television image formed by the image source means along a folded optical path onto the screen when the optical path is erected, and the screen is located a predetermined image projection distance from the image source means. The receiver further includes means for elevating the screen from a first receiver-inoperable position wherein the screen is completely enclosed within the cabinet and the receiver is ultra-compact, to an elevated receiver-operable position wherein the screen is emerged from the cabinet. As a result, the optical path is extended to a length equal to the predetermined image projection distance whereby the projection image is coincident with the screen.
In projection television systems having image projection devices positioned off the axis of the viewing screen, distorted images are projected by the off-axis devices. Two types of optical distortion are present --trapezoidal and horizontal non-linearity. These types are best described by the term "non-linear magnification distortion." In U.S. Pat. No. 4,274,110 of common ownership herewith, means and method are disclosed for compensating for non-linear magnification distortion in projection television systems. The projection television system has a projection screen for displaying a light image cast thereon. The screen is spaced apart from at least one light projection means whose projection optical axis lies at a non-zero, acute-angle A with respect to the screen axis. The light projection means comprises cathode ray tube means having a cathodoluminescent screen on the inside surface of a face panel thereof whose axis is substantially parallel to the projection optical axis. Electron-beam generating means are disposed on the cathode ray tube electron-optical axis for forming an electron image on the cathodoluminescent screen which is converted to a visible image by the cathodoluminescent screen. Lens means on the projection optical axis provide for projecting on the projection screen the light image of the electron-formed visible image. The light image inherently has non-linear magnification distortion attributable to the location of the projection means off the projection screen axis. The system is characterized, according to one embodiment of the invention, by the cathode ray tube electron-optical axis defining a non-zero, acute-angle B with respect to the axis of the cathodoluminescent screen. The value of the angle B and the orientation of the electron optical axis is selected according to the invention to cause the electron-formed visible image to have an orientation and a non-linear magnification distortion effective to substantially compensate for the off-axis-induced non-linear magnification distortion of the projected light image. This patent is fully incorporated herein by reference.